maidroid/maidroid_core/cores/empty.lua

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-- Copyright (c) 2016 tacigar. All rights reserved.
-- https://github.com/tacigar/maidroid
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maidroid.register_core("maidroid_core:empty", {
	description      = "maidroid core : empty",
	inventory_image  = "maidroid_core_empty.png",
	on_start         = function(self) end,
	on_stop          = function(self) end,
	on_resume        = function(self) end,
	on_pause         = function(self) end,
	on_step          = function(self, dtime) end,
})

-- only a recipe of the empty core is registered.
-- other cores is created by writing on the empty core.
minetest.register_craft{
	output = "maidroid_core:empty",
	recipe = {
		{"default:steel_ingot", "default:steel_ingot", "default:steel_ingot"},
		{"default:steel_ingot",    "default:obsidian", "default:steel_ingot"},
		{"default:steel_ingot", "default:steel_ingot", "default:steel_ingot"},
	},
}